One of the remaining mysteries of neuroscience is how memories are stored for periods of days, weeks or years. It has been known for some time that the formation of stable memory requires protein synthesis, a feature of memory common to vertebrates and invertebrates. Protein synthesis localized to the synapse is of special interest because it might confer selective synaptic change and the stable modification of a neural circuit. But how protein synthesis is deployed across the nervous system and contributes to the formation of a particular memory is unclear. We have used fluorescent reporter constructs to visualize synaptic protein synthesis in Drosophila that form a long-term memory. The association of an odor with electric shock was correlated with local protein synthesis that displayed features of synaptic specificity, and the induction of mRNA transport to synaptic regions. These features of memory appeared to be controlled by the RNA- Induced Silencing Complex (RISC) in a pathway involving RISC regulation by the Proteasome. A RISC component, Armitage, was found to be ubiquitinated and degraded in a Proteasome-dependent fashion, evidently contributing to the release of synaptic protein synthesis from RISC suppression. These observations raise a number of questions of importance to understanding the mechanisms underlying memory. Can we build a fine-grained neural map of where protein synthesis occurs as a particular memory forms? Can we build a map of where the regulation of protein synthesis is required? What are the temporal characteristics of synaptic protein synthesis and how are they related to the maintenance of a synapse in a stable new state? We have only begun to understand the role and biochemistry of the RISC pathway at the synapse, but as an evident regulator of these events, we believe this understanding will illuminate the biochemical and cellular mechanisms underlying memory. The strong potential of this study to make clinical contributions should not be overlooked, as it is evident that these mechanisms operate at mammalian and human synapses. This study will likely identify new targets for therapeutic efforts to aid patients with disorders of memory (for example, Alzheimer's Disease) and synaptic activity (for example, epilepsy).

Public Health Relevance

Many pathological and some developmental disorders of the nervous system are associated with defects in the formation, maintenance or recall of memories. Even where the biochemical mechanisms underlying memory are not the primary defect, therapeutic tools to enhance or restore memory would offer considerable benefit to the patient and alleviate the cost and burden of such disorders to society. The work described in this proposal is aimed directly at the characterization of a novel mechanism underlying memory. The description of new biochemical pathways underlying memory offers insights into the design and targeting of therapeutic agents. This project offers considerable potential to benefit patients with memory deficiencies via the eventual development of novel therapeutic agents.